Platinum metal ammino cyanide plating bath and process for electrodeposition of platinum metal therefrom



Patented Feb. 19, 1935 PATENT OFFICE PLATINUM METAL AMMINO cram s PLAT- mo BATH AND rnoosss roa ELEC- sraonnrosrrrou or PLATINUM METAL THEREFROM Edmund M. Wise, Westfleld, N. 1., assignor to The International Nickel Company, Inc.,- New York, N. Y., a corporation of Delaware No Drawing. Application November 20, 1933,

Serial No. 698,928

19 Claims. (01. 201-1) The present invention relates to a process of electrodepositing a platinum metal and more particularly to a process of electrodepositing of platinum, palladium, rodium and alloys thereof and to a bath for carrying the aforesaid processes into practice.

It is well known that in the electroplating of a platinum metal from a bath having a neutral or alkaline character, it has been necessary to employ a salt or a compound which is adapted to give a relatively low platinum metal ion concentration in order to avoid the precipitation of basic platinum metal salts. It has likewise been generally desirable to limit the platinum metal ion concentration to rather low levels for the purpose of permitting the direct plating on less noble metals and to'provide a smooth, non-granular deposit. The lower limit of useful platinum metal ion concentrations is fixed by the cathode current efliciency desired. Thus, for instance, in the case of alkali metal palladium cyanides, the platinum metal ion concentration has been so low that no plate can be obtained. Although many attempts have been made to overcome the disadvantages of prior processes, none, as far as I am aware, has been provided which is wholly satisfactory and successful and whichhas been capable of producing plates acceptable to the trade.

I have discovered a process for electrodepositing a platinum metal and a bath for carrying such process into practice which avoids the disadvantages of prior processes and which provides the art with a satisfactory, reliable and practical bath and procedure for electrodepositing a plate of a platinum metal which is acceptable.

It is an object of the present invention to provide a process of electrodepositing a platinum metal from a bath containing a platinum metal body or substance, herein termed amminocyanide. o

It is a further object of the invention to provide a process of electrodepositing a platinum metal from a bath having a neutral or alkaline 1 character and containing a platinum metal ammono-cyanide.

It is another object of the invention to provide a process of'el'ectrodepositing a platinum metal from an alkaline or neutral bath containing a platinum metal ammino-cyanide.

It is also within the contemplation of the invention to provide a bath for the electrodepositing of the platinum metal containing amminocyanide which is capable of dissolving in dilute aqueous ammonia or other campatible alkali solutions and to ionize therein sufllciently to permit the electrodeposition of a platinum metal.

The invention also contemplates the provision of a process which is capable of effecting-the electrodeposition of a platinum metal upon silver, nickel, copper and various other base metals.

Other objects and advantages of the invention will become apparent from the following description.

According to the present invention, the novel baths used comprise an aqueous solution of an ammino-cyanide or ammino-cyanides of the platinum metal or metals desired. By means of such baths, I have found that I can deposit platinum metals on any of the noble 'metals or noble metal alloys and on such base metals as silver and silver alloys, copper and copper-base alloys, nickel and nickel-base alloys, nickel-silver and so forth. -It may be noted that platinum metal plates deposited from many other types of baths tended to strip from nickel and the like when attempts .were made to deposit heavy coatings of platinum metals upon it. In cases where it is not practicable or possible to plate directly on to the metal surface itself, for example, in the case of iron and steel, a preliminary copper or silver coating. may previously be applied by any suitable method as those skilled in the art will readily understand, and the platinum metal or alloy may subsequently be electro-deposited on the copper orsilver surface by the present improved process.

The term ammino-cyanicle as used herein includes not only compounds containing ammonia, but also the analogous soluble compounds in which the ammonia groups are replaced by an organic amine. Thus, for instance, in the case of platinum and palladium, the preferred compounds as added to the bath areoi the type [M(A)2(CN)2], where M is platinum or palladium and A is NH: or an equivalent organic ammine. These salts while generally of low solubility in neutral solutions are quite soluble in aqueous alkaline solutions. In the case of the alkaline ammoniacal solutions of these salts it is thought to undergo at least partial conversion.

to the closely related tetrammine dicyano platinum metal compound. Of course, this thought is-a mere theory and is not to be binding if subsequent experiment discloses somev other reaction.

For the purpose of giving those skilled in the art a better understanding of the invention the following specific illustrative examples will be given.

For the preparation of palladium salts about 21 grams of palladosamine chloride [Pd(NHs):C12], is dissolved in about 23 c. c. or 0.880 (specific gravity) ammonia and about 40 c. c. oi! water. About 13.3 grams of potassium cyanide is now added and the mixture stirred well for about one hour. The solid salt separating out is filtered oil and recrystallized from about a 2 percent aqueous ammoniacal solution. The recrystallized salt which is dicyano-diammino-palladium, [Pd(NHa)2(CN)a], is in the form of fine white needles and contains about 55.3% 0! palladium.

An aqueous more or less alkaline solution of the aforesaid compound may be used'either for giving thin bright deposits'having a thickness of the order of about 5 to 10 millionths of an inch (1 to 2 mg. sq. in.) or thicker matte deposits of the order of .0005 inch mg. sq. in.). In the former case good results may be obtained It is preferred to use anodes of palladium foil. In the first example, the'bath is usually operated at a temperature or about 40-50 C. though temperatures up to about 90 C. may be employed. The article is plated for about 5 to 10 minutes at a current density of about 0.1 to 0.2 amperes per dcm. (about .92-1.85 amperes per square foot). Exceedingly bright flash deposits have been obtained in the foregoing manner.

In the second example, the bath is operated under similar conditions for a longer time depending on the thickness of the plate required. The current efilciency, calculated on the basis of divalent palladium, was found to be about 66 percent (6070%).

The corresponding platinum salt, which contains about 69.37% platinum is prepared as I01- lows:

About 22.7 grams of ammonium chloro-platinate, (N114) :PtCls, and about 8.6 grams of ammonium oxalate, (NH4)2C2O4 are mixed with about 54 c. c. of water and heated in a conical flask on a water lath. After about one hour it was diluted to about 216 c. c. and heated for about 2 hours longer. The volume then was about c. c. The solution was cooled and then packed in ice at about 0 C. and about 51 c. c. of 1:1 ammonium hydroxide was added and the solution kept at about 0 C. over night. A salt was precipitated which is yellow but was made somewhat green by the presence of Magnus salt. The mixture was filtered and the almost colorless filtrate was discarded. The salt was recrystallized from about 4% H01 solution and the green salt was separated by filtration. The salt was dried in an oven at 100 C. This salt was dichloro diammino platinum. It was suspended in 30 me. of a 10% NHiOH and about 2.90 grams of solid KCN added to convert the salt to dicyano diammino platinum. on heatmg the whole mass becomes a solid. It was diluted to about 300 c. c. and heated to boiling and the solution filtered free from the small amount oi. brown insoluble material. White crystals immediately commence to separate from the filtrate and the bulk was considerably increased by rapid cooling to room temperature. The crop of white salt was filtered, washed with a little cold water and dried in an oven at about 100 C. The dried white salt was considered to be dicyano-diammino platinum. This salt is less soluble in aqueous ammonia than the palladium salt, and the plating bath consists oi about 5% ammonia solution saturated at about 30 C. with the salt. Anodes oi platinum or palladium toil were used. The bath was operated at a temperature of about 40 to 80 C. ,and the best results were obtained at about 70 C. Articles were plated for periods of about 15 to 30 minutes using a current density 01 up to about 0.4 amperes per dcm. (about 3.7 amperes per square foot). The current efllcien'cy ior'divalent platinum was about 5 percent.

In the case of rhodium, the salt was prepared from chloro-pentammino rhodium chloride [RI-UNHanCllCh. For example about 15 grams of chloro-pentammino rhodium chloride was dissolved in a boiling solution of about c. 0. containing about 4.5 grams of NaOH and about 4.0 grams KCN. It was stirred vigorously and boiled until the reaction went to completion. The pale yellow solution was cooled and filtered. The cold filtrate was neutralized with about a 1:1HNOa solution which required about 19 c. c. 01 the acid. The solution was slowly evaporated to about 87 c. c., cooled and treated with an equal volume of concentrated nitric acid. The crop of crystals of impure complex cyano ammine was filtered oil, the filtrate being discarded. The salt is purified by dissolving in about c. c. of boiling water and then filtered. This solution was concentrated until crystals appeared and then cooled. To the cooled mixture an equal volume of concentrated nitric acid was added. The moist salt was the nitrate of the complex amine and was converted to the sulphate by dissolving in about 250 c. c. of boiling water. About 6.5 c. c. of about a 1:1H2s04 solution was added and the cooled mixture poured into about 650 c. c. of methyl alcohol to precipitate it. The salt may be further purified by repetition oi the alcoholic precipitation. The bath is prepared by dissolving the requisite quantity of the salt in water to give about 5 grams per liter of rhodium. Anodes of platinum and palladium were employed. Temperatures up to 90 C. may be used. but the preferred range is 50'70 C. Current densities up to about one ampere dcm. were employed and the current eificiency calculated for trivalent rhodium were of the order of about 10-25%. The depositing of rhodium causes the liberation of ammonia on account of the discharge of the complex cation (N'HahBh and consequently the solution tends to become alkaline. To prevent this the solution may be buffered with sodium di-hydrogen phosphate and sodium monohydrogen-phosphate, although at the usual working temperature most of the ammonia evaporates oil.

The baths may in all cases be replenished by the addition of the corresponding salt of the platinum metal being deposited as is used in the initial preparation of the bath.

The use of a mixture of pure complex salts in the bath leads to the deposition of alloys oi! the composite metal.

It is to be observed that in the event that a still further lowering of the platinum metal ion line solution and that the term aqueous solution as used in the specification and claims is in-- tended to cover water and solutions thereof.

Although the present invention has been described in connection with certain preferred embodiments thereof, it is to be understood that variations and modifications may be resorted to which will be within the purview of the appended claims.

I claim:

l. A process of electrodepositing a platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal.

2. A process of electrodepositing a platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal andconducting the aforesaid operation at a temperature up to about 90 C.

3. A process of electrodepositing a .platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal and conducting the aforesaid operation at a temperature of about 40to about 90 C.

4. A process of electrodepositing a. platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal and maintaining a current density of about 1 to about 10 amperes per square foot in conducting the aforesaid electrolyzing operation.

5. A process of electrodepositing a platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal and maintaining the platinum metal content of the aforesaid solution by adding an amount of a platinum metal ammino-cyanide equivalent to the amount of platinum metal electrolyzed from the solution.

6. A process of electrodepositing a. platinum metal which comprises electrolyzing an aqueous solution containing an ammino-cyanide of a platinum metal and maintaining a solution in a non-acid condition.

7. The process set forth in claim 1 in which dicyano-diammino-palladium or dicyano-diammino-platinum is added to the solution to supply the platinum metal to be electrodeposited.

8. The process set forth in claim 1 in which the solution contains a rhodium compound pro-' duced by rendering alkaline a solution of chloropentammino-rhodium chloride, treating this solution with an alkali cyanide or hydrocyanic acid.

and acidifying with a mineral acid and isolating the resulting salt.

9. A bath for the electrodeposition of a platinum metal which comprises an ammino-cyanide of the platinum metal to be deposited.

10. A bath for the electrodeposition 01 a platinum metal which comprises an ammino-cyanide of the platinum metal to be deposited and a conducting salt. I i

11. A bath for the electrodeposition of a platinum metal which comprises an ammino-cyanide oi the platinum metal to be deposited and an alkali salt for improving the conductivity oi. the solution. 7

12. A bath for the electrodeposition of a platinum metal which comprises an ammino-cyanide of the platinum metal to be deposited and an alkali or an alkaline salt of the group consisting of ammonia, sodium and lithium.

13. A bath for the electrodeposition of a platinum metal which comprises an ammino-cyanide of the platinum metal to be deposited, said bath having a non acid character.

14. A bath for the electrodeposition of a platinum metal which comprises an ammino-cyanide of the platinum metal to be deposited and a bufier salt to prevent the solution from becoming too alkaline.

15. A bath such as set forth in claim 9 which is used for striking a base metal prior to heavy platinum metal plating.

16. A bath such as set forth in claim 10 whichis used for "striking a base metal platinum metal plating.

17. A bath such as set forth in claim 11 which is used for striking a base metal prior to heavy platinum metal plating. v

18. A bath such as set forth in claim 9 which contains an excess of CN which is used for striking" a base metal prior to subsequent heavy plating with a platinum metal. .i

19. A bath for the electrodeposition of platinum metal alloys which comprises an amminoprior to heavy cyanide oi the platinum metals to be deposited.

EDMUND M. WISE. 

